Video recording control and synchronizing system



June 25, 1968 R. J. YOUNGQUIST VIDEO RECORDING CONTROL AND SYNCHRONIZINGSYSTEM Filed April 21, 1966 7 j vIDEo VIDEO VIDEO HEAD BIAS BIAS UNDSIGNAL AMPLIFIER TRAP OSCILLATOR SIGNAL- 54 6'7 6'0 1 .90 I, I 95 L. m

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STRIPPER INTEGRATOR COMPARATOR LEAD NETWORK 58 c AND AMPLIFIER +l2V 51.1. 56 7 v A I SYNC. PULSE 74' SYNC. HEAD r76 52 AMPLIFIER DRIVER H .251 72 t 6,4 6,29 .204 t I 1w J2 J4 l PRE- PHASE VIDEO ilfigMP I 'EouAL-AMI? n, AMPL'F'ER IZER BLANKING I] I 1/ I? g UNIT J5 J g M 27 T 10;

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'8 PQEA-krd f oa/umpwsr J14 x 44 BY June R. J. YOUNGQUIST VIDEORECORDING CONTROL AND SYNCHRONIZING SYSTEM Filed April 21, 1966 5Sheets-Sheet 2 I2 v e .150 5'1; M VIDEO BIAS VIDEO VIDEO 1 OSCILLATORSIGNAL AMPLIFIER 14$ J 146 39 12? 7 SYNC SOUND STRIPPER SIGNAL 6.9 .91INTEGRATOR 7 r BIAS RECORD OSCILLATOR AMPL'F'ER 6.4 67 4 16 r5 Ag) 5 5'5242 Z44 rl 81 6'6 16 29 ONE SHOT 246' L. AMPLIFIER MULTI- 245' ggURCE 2vVIBRATOR 97 I o T I167 [74 1:6 22:1;- f DRIVER INVENTOR.

June 5, 1968 R. J. YOUNGQUIST ,3

VIDEO RECORDING CONTROL AND SYNCHRONIZING SYSTEM Filed April 21, 1966 5Sheets-Sheet 3 57% +|2 V J07 64 2 OUTPUT PREAMPLIFIER t 2102 f 275 JCB254 16 G5 65' 105' VIDEO AMPLIFIER r278 so smc. A ONE SHOT STRIPPERMULTI- VIBRATOR -|2v 59a ONE SHOT f F243 1 VIBRATOR COM PARATOR LEADNETWORK AND AMPLIFIER MW MM A770P/UEPS June 25, 1968 R. J. YOUNGQUIST3,390,231

VIDEO RECORDING CONTROL AND SYNCHRONIZING SYSTEM Filed April 21, 1966 5Sheets-Sheet 6610/57 FM /4 TUE/V575.

I 490 1540 warn/0px 4N0 mm mm M ME/Wm? ROBE/P711 You/v COMPAQ/6470BV1050 I flMPUF/EK I l l I I I L United States Patent 3,390,231 VIDEORECORDING CGNTROL AND SYNCHRONIZING SYSTEM Robert J. Youngquist, Viliageof Arden Hills, Minn assignor to Minnesota Mining and ManufacturingCompany, St. Paul, Minn, a corporation of Delaware Continuationdn-partof application Ser. No. 373,365, June 8, 1964. This application Apr. 21,1966, Ser. No. 544,167

10 Claims. (Cl. 17S--6.6)

ABSTRAQT THE DKSQLQSURE A video tape transducing apparatus of the typein which a tape has a video signal recorded in a series of obliquetracks and a control signal recorded along one longitudinal edge of thetape is shown wherein the tape is driven longitudinally at a constantspeed adjacent a transducing head which is rotated obliquely to thelongitudinal direction of the tape and at a relatively high speed andduring playback a first pulse signal generated by each revolution of thehead is used for synchronizing track position and head position in aservo system which controls a braking member and a second pulse signalgenerated by each revolution of the head is used for supplying avertical synchronizing signal to the video signal reproduced from thetape by the head.

This is a continuation-in-part of application Ser. No. 373,365, filedJune 8, 1964.

The present invention is concerned with improved transducing apparatusfor recording high frequency signals and in one aspect to apparatussuitable for recording television signals and the like.

Various arrangements have been proposed in the past for recording highfrequency signals or television signals comprising video signals havingpicture signals, synchronizing signals and blanking signals withseparate audio signals. In some cases, the entire television signal hasbeen recorded longitudinally along a tape. Due to the very highfrequencies involved, it is necessary to have a tape moving at very highspeeds and the total amount of tape thus necessary in order to record aprogram of any length becomes very high. It has also been proposed toemploy a system in which the recording head is moved at right angles tothe tape as the tape is moved longitudinally. In order for this systemto be feasible, it is usually necessary to employ a plurality of headswith a rather complicated switching arrangement for sequentially usingthe signals recorded by the several heads and eliminating theoverlapping portions of the signals recorded by the different heads. Ithas also been proposed to employ a recording system in which the tape ishelically disposed over a drum carrying a recording head. The drum isdriven at a relatively high speed as compared with the speed of thetape. This results in a series of oblique tracks, each of which is muchlonger than the width of the tape. With this system, it is possibleusing a single head and not excessively high speeds to record an entirefield as the head passes from one edge to the opposite of the tape.

My invention is concerned with a transducing system in which the headmoves obliquely to the longitudinal direction of the tape, and in oneembodiment to a sys tem in which the tape extends helically over therecording head. From the teachings of this invention, a relativelysimple recorder employing such a transducing system avoids certain ofthe disadvantages present in recordersof the prior art. Many of theseprior art arrangements have been quite complicated. The presentinvention may be utilized to develop a recorder for television signals3,390,231 Patented June 25, 1968 which is relatively inexpensive so asto make it possible to utilize the same economically for noncommercialrecording of television programs. The television signals comprise videosignals having picture signals, synchronizing signals and blankingsignals and separate associated audio signals.

In order to provide an economical relatively simple recorder fortelevision signals, a number of novel features are employed. In thefirst place, in order to employ the expedient of a head rotatingobliquely to the direction of tape travel, it is necessary to controlaccurately the synchronization of the head position with the incomingvideo signal. I accomplish this during the recording operation bygenerating a pulse signal indicative of the position of the head. Thepulse signal is compared at a novel comparator circuit with asynchronizing signal derived from the video signal which synchronizingsignal is recorded as a control signal along one edge of the tape whichis first erased. During playback, the recorded synchronizing controlsignal is reproduced and compared with a pulse signal indicative of headposition and through the novel comparator circuit, the synchronizationof the head position with the tract position of the video signal ismaintained.

One of the features of this invention is that in one embodiment thepulse signal indicative of the head position is used not only to controlthe synchronization of the head position with the recorded synchronizingsignal but it is used to supply a vertical synchronizing signal toreplace that lost when the edge of the tape was erased.

Another feature of my invention is that in another embodiment the pulsesignal indicative of the head position is used to synchronize the headposition with the recorded synchronizing signal while a clamp pulsesignal, produced after the head position pulse signal was produced, isused to replace the vertical synchronizing signal lost when the edge ofthe tape was erased.

A still further feature of my invention is that in one embodiment thepulse signal indicative of head position is used to blank out the signalfrom the reproducing head as it passes the edges of the tape on whichthe control signal and audio signals are recorded.

In another embodiment, a clamp pulse, produced after the head pOsitiOnpulse signal, is used to blank out the signal from the reproducing headas it passes the edges of the tape.

A further feature of my invention is that low frequency components lostduring recording due to the high relative speeds between the head andtape are replaced during reproduction with novel clamping circuits.

A still further feature of this invention is that the television signalscan be recorded directly and without frequency modulation as isconventionally utilized in recorders wherein the head moves at an angleoblique to the direction of movement of the tape.

A still further feature of this invention is a novel support for arecording head having means to insure close contact between therecording tape and the head despite high speed relative movement betweenthe tape and head.

Further features of this invention will become apparent from aconsideration of the accompanying specification, claims, and drawing ofwhich:

FIGURE 1 is a schematic view of the recording portion of the apparatuswith the various circuit components being shown in block diagram form;

FIGURE 2 is a view of the reproducing or playback portion of theapparatus with the same type of showing as in FIGURE 1;

FIGURE 3 is a schematic view of the recording portion of the apparatuswith certain novel circuit components of the invention being shown incircuit form;

FIGURE 4 is a schematic view of the reproducing or playback portion ofthe apparatus in which, as in FIG- URE 3, various circuit components ofthe invention have been shown in circuit form;

FIGURE 5 is an isometric view of the rotating drum over which the tapeis passed;

FIGURE 6 is a top plan view of a portion of the drum showing in moredetail the location of the record ing and reproducing head and certainauxiliary slots associated therewith;

FIGURE 7 is a side View of the same portion of the drum;

FIGURE 3 is a schematic diagram, partially in biock form, illustratinganother embodiment of a recording system utilizing the comparator in adifferent arrangement than that of FIGURE 3; and

FIGURE 9 is a schematic diagram, partially in block form, illustratinganother embodiment of a reproducing system utilizing another clampingcircuit.

Referring to FIGURE 1 of the drawing, 1 have shown in schematic form oneembodiment of the recording portion of my apparatus. A magnetic tape 14}is mounted on the supply reel 11. After leaving the supply reel 11, thetape passes a cylindrical guide post 12, being held against the guidepost by a spring loaded felt member 13. The tape then passes over aninertia roller 14 and from there helically over a rotating drum 15 whichcarries the transducing or recording and reproducing head 16. Theconstruction of the drum 1S and the head 16 are best shown in FIGURES 5,6 and 7 and will be described later. After leaving the drum 15, whichwill be discussed in more detail later, the tape it) passes over a headassembly 17 comprising erase heads 18 and 1), a sound recording head 26and a synchronizing signal head 21. The tape next passes between acapstan 22 driven by a motor 23 and a pressure roller 24. The tapefinally passes onto a take-up reel 26 driven by a motor 27. The motor 27drives the take-up reel 26 at a speed such that the tape tends to bedriven at a somewhat higher speed than it is driven by the capstan 23. Asuitable slip connection (not shown) is provided between the motor 27and the take-up reel 26 to allow for this difference in speed. Therelative speed at which the take-up reel 26 tends to move the tape ascompared to that at which it is driven by the capstan 22 varies, ofcourse, with the amount of tape on the take-up reel.

The drum is driven by a suitable induction motor 28 having a fieldwinding 29 and a rotor 30. Field winding 29 is connected to lineconductors 31 and 32 leading to a suitable commercial source ofalternating current power. The motors 23 and 27, driving the capstan 22and the take-up reel 26 respectively, are likewise connected to lineconductors 31 and 32. The shaft of the motor 28 has a relatively largepulley 34 which has a belt 35 thereon extending over a relativelysmaller pulley 36 secured to a shaft 38 of a braking motor 39. The shaftof the braking motor is in turn secured to the shaft 40 of the drum 15.The braking motor 39 comprises a conventional squirrel-cage rotor 42 anda field Winding 43. Interposed between the rotor 42 and the pulley 36 isa flywheel 44 for stabilizing the speed at which the drum 15 is drivenby motor 23 and braking motor 39.

As will be pointed out in more detail later, the motor 28 tends to drivethe drum 15 at a speed somewhat higher than desired. The winding 43 ofthe braking motor 39 is supplied With a direct current voltage from asource 46 under the control of apparatus to be presently described. Verybroadly, the application of direct current to winding 43 tends to causea braking effect to be present to reduce the speed of the drum 15 belowthat at which it would normally be driven by motor 28 through the belt35. The DC. energization of winding 43 is adjusted in accordance Withthe comparative position of the 6 Tim and the incoming video signal tomaintain a L s1.

relationship so that the head 16 passes diagonally from one edge of thetape to the opposite edge at the end of each field of the video signal.

Referring now to the energization of the head 16, a video signal 56 maybe derived from a television receiving set. This signal is taken off ofthe set at a point sub sequent to the video detector and prior to thetime that the video signal is applied to the picture tube of the set.The video signal comprising a picture signal horizontal synchronizingpulses and vertical synchronizing pulses is first passed through a videoamplifier 51 and from there through a video head driver 52. This headdriver is designed to provide suitable pro-emphasis and will bedsecribed in more detail later in connection with PEG- URE 3. From thehead driver, a signal passes through a bias trap 53 where it has addedto it the output of a video bias oscillator 54. in one embodiment of myapparatus, this video bias oscillator is tuned to provide an output of 7megacycles per second. The bias trap 53, which will be referred to inmore detail later, is tuned to be resonant at this frequency and toblockthe output of the bias oscillator from being applied to the head driver.The combined output of the oscillator and the amplified video signalpasses through a conductor 56 to the record contact 57 of a switch 58having a movable contact member 59 and a further fixed playback contact60. Since FIGURE 1 shOWs the apparatus in the record cycle, the movableswitch contact 59 is in engagement with the record contact 5'7. From themovable switch contact 59, the current passes to one terminal of oneWinding 63 of a coupling transformer 64, the other terminal of which isconnected to ground at 66. The coupling transformer 64 has two windings63 and 65 which are Wound concentrically. The Winding 63 is a stationarywinding whereas the Winding 65 moves with the drum 15. By means of thetransformer 64, it is possible to couple the head 16 to either an inputsignal (in the record cycle) or to output means (in the play backcycle). The Winding 65, which revolves with the drum 15, is coupled tothe head 16.

It will thus be seen that the video signal 56 is amplified, is modifiedby the bias oscillator 54, and is then applied through the transformer64 to the head 16. This video signal is, in turn, recorded on the tapeas the drum 15 revolves and the tape it is driven longitudinally at aconstant speed. As previously mentioned, the drum is controlled so as torotate in the same direction as the tape is driven and at such a ratethat the head moves from one edge of the tape obliquely across the tapeto the opposite edge during a time equal to one field of the videosignal.

The output of the video amplifier 51 is also connected through aconductor 67 to a synchronizing signal stripper 68 of conventional type.This stripper is commonly referred to as a sync stripper and will be soreferred to in the subsequent specification. The output of sync stripper68 is connected through a conductor 69 to the output of the head driver52 in order to introduce the amplified synchronizing signal into thesignal being supplied to head 16, reinforcing these synhronizingsignals.

The output of the sync stripper 68 is also connected to an integrator 74to derive from the sync signal a vertical sync signal. This verticalsynchronizing signal is used in two ways. in the first place, the outputof integrator 70 is connected through conductor 72 to a sync pulseamplifier 73. This sync pulse amplifier will be described in more detaillater. The output of the sync pulse amplifier as in turn connected to async head driver 74 and the output of this sync head driver 74 isconnected through a conductor "/6 to the synchronizing signal head 21,which is eiiective to record this synchronizing signal as a controlsignal along one edge of the tape.

The output of the integrator 7% is also connected to a comparator '79which receives not oniy the vertical synchronizing signal, but also asignal which is indicative of the speed at which the drum is rotated.Located within the drum 15 in one end thereof is a permanent magnet 81).Located adjacent to the drum, closely adjacent to the path of the magnet80, is a typical magnetic pickup head 81. Each time that the magnet 80passes the head 81, a pulse is produced in the output of head 81. Thispulse is passed through a pulse amplifier 82. and connected throughconductor 83 to the comparator 79. The comparator thus receives not onlythe output of integrator 79, but also receives the output of amplifier32 which is a pulse output indicative of the speed at which the drum 15is being rotated. The output of comparator 79, which depends upon therelative values of the two signals fed to it, is connected to a leadnetwork and amplifier 85. This amplifier and network, which will bedescribed in more detail later, serves to amplify the output of thecomparator and to introduce a certain lead factor to reduce hunting.This output is connected through a conductor 86 to the winding 43 andserves to control the amount of direct current supplied by source 456 towinding 43. The more direct current that flows through winding 43, themore will be the braking effect that is exerted by the braking motor 39.As will be more apparent from the subsequent description, this brakingeffect is so adjusted as to maintain a desired synchronization betweenhead position and the video signal.

The sound is recorded along the opposite edge of the tape from thesynchronizing control signal by head 29. The sound signal 39 derivedfrom the television set is applied through a record amplifier 90 to therecord head 20. Connected between the record amplifier 99 and the recordhead 21 is a sound bias oscillator 91 which functions in the usualmanner to superimpose upon the signal applied to the head 2%) a signalhavin a frequency such as to provide the desired bias to the signalapplied to the tape.

Erase heads 13 and 19 are provided for erasing along the edges of thetape 10 where the control and sound signals are to be applied. The erasehead 18 is connected to the output of the bias oscillator 91 to apply ahigh frequency alternating current to the erase head 13. The erase head19 is connected to a direct current source 93, it being more desirableto use a direct current for erasing along the track where a controlsignal is to be recorded.

Very briefly summarizing the operation of the record apparatus, thevideo signal is amplifier and has superimposed thereon the usual biassignal. Also superimposed on the video signal is the output of the syncstripper which serves to reinforce the synchronizing signals. Thiscombined signal is applied to the stationary winding of transformer 64,the output of which is applied to head 16. The speed of the drum 1.3 ismeasured by means of the head 81 which is associated with the magnet 80carried by the drum 15. The pulse signal produced in this head 81 iscompared with the integrated signal from the sync stripper so as tocompare the position of the head 16 with that of the video signal toinsure that the head passes the edges of the tape at the end of eachfield of the video signal. The integrated output of the sync stripper isalso applied through an amplifier and a head driver to the head 21 torecord along one edge of the tape, a signal which is essentiallyindicative of the track position of the video signal. The sound signal89 is amplifiecl in the usual manner and has applied thereto a suitablebiasing oscillator. The combined signal is applied to the soundrecording head 21). Previous to the tape passing by the sound head andthe synchronizing signal head 21, the portions of the signals alongthese edges of the tape are erased by erase heads 18 and 19. As will bepointed out in more detail later, only a small portion of the actualvideo signal is erased, most of the signal being erased being thevertical synchronizing signal. As previously pointed out, the speed ofthe head is such that it completes one field each revolution of the headand the apparatus is so operated that the head passes from one edge ofthe tape to the opposite edge of the tape at the end of a field wherethe vertical synchronizing signal is located. As will be further pointedout in connection with the record cycle, l have provided means forreplacing the vertical synchronizing signal which is lost in therecording process.

Turning to FIGURE 2, I have shown schematically one embodiment of anapparatus utilizing the teachings of this invention for reproduction orplayback of the recorded signals. The mechanism for driving the tape isexactly the same, as is the drum 15. Consequently, the same referencenumerals have been applied in this figure as were employed in FIGURE 1.It is, of course, understood that the apparatus employs a number ofswitches for switching over from the record to the playback cycle andthese switches, with the exception of switch 58, are not shown in thisfigure in order to simplify the description and facilitate a more readyunderstanding of the general operation of the apparatus. The switch 58,which was referred to in connection with FTGURE 1, has a movable switchblade 59 shown in engagement with the playback contact 69 instead of therecord contact 57. Other than this, none of the switching connectionsare hown.

As the tape it passes over the drum 15, which is re volving at arelatively high speed, the signal picked up by head 16 is conveyed tothe rotary winding 65' of the coupling transformer 64. The signal isaccordingly induced in the stationary winding 63 which, as in the recordcycle, has one end grounded and the other end connected to the movableswitch contact 59 and passes through the playback contact dd to theprimary winding 100 of a step-up transformer 101. This transformer has afour-to-one ratio and acts to quadruple the relatively small voltageoutput of the head 16. The secondary winding 10?. of this transformer191 is connected to a pre amplifier 103 which may have incorporated init certain pre-emphasis networks in the conventional manner. From thepreamplifier, the signal is passed to a phase equal izer 1414 which willbe described in more detail later. This phase equalizer is designed tocompensate for the shift in phase in the transmission of the variouscomponents of the signal due to differences in frequencies of thesecomponents. From the phase equalizer, the signal goes to a videoamplifier 1% and from there to a clamp and blanking unit 196. This clampand blanking unit forms a very essential part of my apparatus and willbe described in more detail later. For the present, it can be statedthat this unit serves to clamp the signals to restore certain lowfrequency components. It also serves through the signal derived fromhead 81 associated with magnet to blank out the portion of the signaldue to the head passing over the edges of the tape along which the soundand control signals are recorded. These two signals would, iftransmitted to the video output, create disturbance since they are notproperly part of the video signal. Furthermore, the clamp and blankingunit also serves to reinsert the vertical synchronizing signal, which,as previously explained, was lost during the recording process. Theoutput of the clamp and blanking unit 10 5 is, as a result of thevarious steps taken therein, a video signal capable of being applied toa video output device such as a picture tube to produce a picturerelatively free from distortion and with the vertical synchronizingsignal replaced. The numeral 107 is used to designate a suitable videooutput device.

The output of head 81, which again is indicative of the speed at whichdrum 15 is being driven, is supplied through the amplifier 82 to theclamp and blanking unit 106 to perform the steps just described. Theoutput of amplifier 82 is also supplied to the comparator '79.

The synchronizing head 21 serves to pick up the control signal recordedalong the edges of the tape scanned by it and this output is connectedthrough a conductor 112 to an amplifier 113, the output of which is connected through a second conductor 114 to the compara tor 79. Thus, thecomparator 79 has supplied to its a signal from the head 81 indicativeof drum position and a signal from head 21 indicative of the trackposition of the video signal. Again, the comparator acts to comparethese signals and produce an output dependent upon the relative valuesof the two signals supplied to it. This output controls the amount ofcurrent supplied from the direct current source as to the winding 43 ofbraking motor 39 to control the speed at which the drum is driven by themotor 23. Thus, the comparator is used to maintain the desiredsynchronization between the position of the head and the track positionof the video signal.

The sound head 29 picks up the signal recorded along the sound track andsupplies this through an amplifier 198 to a suitable audio output device109. The operation of the audio signal is otherwise entirelyconventional and needs no detailed explanation.

In connection with FIGURES l and 2, I have described the generaloperation of one embodiment of a record and playback portion of myapparatus. In FIGURES 3 and 4, I have shown the circuit details of anumber of the components, which were shown in block diagram in FIGURES land 2 for the purposes of simplicity. Inasmuch as an understanding ofsome of these circuit components is necessary to a completeunderstanding of the novel features of my invention, reference will nowbe made to FIGURES 3 and 4.

DESCRIPTION OF FIGURE 3 Referring first to FIGURE 3, I have again shownthe source of video signal 5t and the video amplifier 51 in blockdiagram form since, as previously pointed out, there is nothing uniqueabout these units. I have, however, shown the head driver 52 in circuitform. This head driver comprises a pair of transistors and 116.Transistor 115 is a PNP transistor having a base 118, an emitter 119 anda collector 120. Transistor 116 is an NPN transistor having a base 122,an emitter 123 and a collector 124. The two transistors 115 and 116 areconnected in a complementary emitter-follower circuit. The emitters 119and 123 are connected together to a common output terminal 126. The twobases 118 and 122; are likewise connected together. A resistor 128 isconnected between the common junction of the bases and ground. Theoutput of the video amplifier 51 is connected through a blockingcapacitor 129 to this common junction of the two base electrodes so thatthe input is applied between this common junction and ground acrossresistor 128.

The collector of transistor 115 is connected through a resistor 130 to aconductor 131 leading to a suitable source of negative potential. In oneparticular embodiment of the invention, conductor 131 was connected to apoint twelve volts negative with respect to ground. The collector 124 isconnected through a resistor 133 to a conductor 134 leading to a sourceof potential positive with respect to ground. In the same embodimentreferred to previously, this conductor 134 was connected to a source ofpotential twelve volts positive with respect to ground.

The amplifier circuit comprising transistors 115 and 116 constitutes, ineffect, two emitter-follower circuits connected back to back and henceresults in a low source impedance regardless of which direction thesignal is changing.

The output of the amplifier as measured between output terminal 126 andground is connected through a preemphasis network 136. This networkcomprises three parallel branches, one consisting of merely a resistor137, another of a resistor 13% and a condenser 139, and a third of aresistor 14% and an inductor 141. The network 136 serves to emphasizelower frequencies and higher frequencies. These frequencies tend to beattenuated in the recording action and it is desirable to emphasize themprior to recording.

Referring to the operation of the pro-emphasis network 136, the lowerleg of the network has a relatively low impedance at low frequencies.This is due to the fact that the impedance offered by inductor M1 isvery low for low frequencies so that the impedance is primarilydetermined by the resistance of resistor 140. As the fre quency of thesignal increases, however, the inductor 141 offers an increasing amountof impedance and the impedance of the network is determined to a largeextent by the impedance of resistor 137 in the upper leg. As thefrequency reaches a higher range, however, the condenser 139 offers lessand less impedance and the impedance of the total network again dropsbecause of the low impedance of the leg including condenser 139. Thus,the impedance network 136 offers a low impedance to both low frequencyand high frequency signals and oifers a substantially higher impedanceto signals in an intermediate frequency range. In this way, emphasis isplaced upon the low frequency and high frequency signals which wouldtend to be attenuated during the recording.

The amplified video signal, after it leaves the unit 52, including theamplifier just described and the pie-emphasis network 135, has added toit a signal from the sync stripper 68 which is connec ed by conductor 69to the junction point 144, to which is connected the output of the headdriver 52. As previously pointed out, the effect of adding a signal fromthe Sync stripper is to reinforce the synchronizing signal whichsubsequently becomes somewhat attenuated due to the clamping actioncmpioyed during the reproducing cycle.

From junction point 144, the video signal combined with the output fromthe sync stripper. 63 passes through the bias trap 53. This bias trapconsists of an inductor 146 and a variable capacitor 147. The inductanceand capacitor 147 form a resonant network which is tuned to thefrequency of the bias oscillator. The function of the bias trap 53 is topermit the video signal to pass through but to prevent the signal fromthe bias oscillator 54 from being grounded through the sync stripper orthe head driver 52. At the terminal 14$, on the output side of the biastrap 53, the video signal has added thereto the signal from the biasoscillator 54. The bias oscillator is supplied with power from conductor131 leading to the source of negative potential through a rheostat 150.From junction point 149, the combined outputs of the video head driver52, the sync stripper 68 and the bias oscillator 54 pass throughconductor 56, contact 57, and movable switch contact 59 to thestationary winding 63 of coupling transformer 64. The movable winding 65of this coupling transformer is connected to head 16 as previouslydescribed.

The signal that is being supplied to the synchronizing signal head 21 torecord a control signal on one edge of the tape will now be considered.As described in connection with FIGURE 1, a signal from the syncstripper 53 is passed through an integrator '78 to produce a verticalsync signal. This vertical sync signal passes through conductors 2G5 and72 to the input of the sync pulse ampliher. This sync pulse amplifiercomprises a transistor of the NPN type. The transistor 155 has a base156, an emitter 157 and a collector 158. A resistor 159 is connectedbetween the collector 15S and. ground and it is the upper terminal ofthis resistor that constitutes the output terminal of the synchronizingpulse amplifier 73. The emitter 157 is connected through a resistor 161to a conductor 162 leading to a suitable source of negative potential.In one particular embodiment of my invention, this conductor wasconnected to a source of potential at minus twelve volts. Connectedbetween conductor 162 and the base 156 is a resistor 163 which isbypassed by a diode 154 which is so disposed as to pass current onlyfrom conductor 1 52 in the direction of the base 156. The incomingvertical syncl'ironizing pulse is coupled to the base 156 through ablocking condenser 166. The peaks of the synchronizing pulses arepositive in polarity and when applied to the base 156 raise thepotential of the base with respect to that of the emitter 157 to causethe transistor to conduct current through the output resistor 159 andcollector 158, emitter 157 and resistor 161 to conductor 162. Thefunction of the diode 164 is to provide a clamping effect. The gain ofthe various amplifiers between the output of the video amplifier 51 andthe synchronizing signal head 21 is such that the signal applied to thesynchronizing pulse amplifier can be limited in both the negative andpositive directions. In order to provide a uniform signal, the clampingdiode 164 serves to clamp the base line of the signal to a minus twelvevolt value. The output pulses of the synchronizing pulse amplifier '73are limited in a positive direction by saturation of the transistor 155.Thus, the output of amplifier 73 is limited in both the positive andnegative directions and a rectangular voltage of uniform wave form isapplied to the sync head driver '74. While I have not shown details ofthis sync head driver, it is to be understood that this may include afurther clamping circuit which operates to clamp the base line of thepulse signal to ground.

From the sync head driver, the signal passes through a fixed recordcontact 168 of a changeover switch 169 having a movable contact 17d anda fixed playback contact 171. It is to be understood that all of thevarious changeover switches may be gauged together. Thus, movablecontact 176 is mechanically connected to the movable contact 59 so as tobe operated simultaneously therewith. From the movable contact 170, thesynchronizing pulse signal passes through conductor 76 to thesynchronizing signal head 21 so that a series of abrupt pulses arerecorded along the edge of the type.

The operation of the comparator circuit 79 and the lead network andamplifier 85 will now be considered.

As previously pointed out, the head 81 located adjacent to the magnet 8%carried by the drum generates a pulse each time that the drum 15completes one revolution. This pulse is amplified by amplifier 82 andpassed through a one-shot multivibrator 175. This one-shot multivibratormay contain two stages but for purposes of simplicity is shown as asingle multivibrator. The resulting output of the multivibrator is arectangular Wave shown applied to the junction point 176. As indicatedthe wave is rectangular having negative pulses 177, the leading edges ofwhich are spaced from each other by a distance depending upon the speedof the drum 15. These pulses are applied to the base 173 of a PNPtransistor 179 having, in addition to base 173, a collector 180 and anemitter 181. Connected between the input point 176 and the collector 180is a condenser 182. The collector 180 is connected through a resistor153 to a conductor 184 leading to a source of negative potential. In oneparticular example, I employed a source of potential at minus twelvevolts. The emitter 181 is connected to a conductor 185 which isgrounded. A diode 186 is connected between the base and ground to clampthe base line of the applied voltage to ground and insure that at notime the base line voltage exceeds ground potential.

Prior to the application of a negative pulse to the base 178, thecondenser 13?. is initially charged through the circuit includingcondenser 182 and resistor 183. When the condenser discharges, due tothe application of the negative pulse, the potential of the base islowered with respect to that of the emitter 181 to cause the voltagedrop across the emitter and collector to gradually decrease. As soon ascondenser 182 is fully discharged, the resulting voltage drop across theemitter and collector is constant until the pulse terminates. Thecondenser 182 then starts to charge gradually, increasing the voltagedrop across the emitter 181 and collector 1%. The result is atrapezoidal wave form in which the emitter collector voltage falls off,flattens out and then increases again.

This voltage is then applied to the base of a further PNP transistor 1%,the collector of this transistor being connected to the conductor 134leading to the negative source of potential. The emitter of transistor1% is connected to ground through resistor 196. The voltage produced bythe varying conduction of transistor 179 appears across resistor 1%between terminal point 192. and ground conductor 185. The resulting waveform 193 is trapezoidal and positive. The beginning of the initial.slope of each trapezoidal peak is determined by the initiation of thepulse 177. The end of the fiat portion of each pulse is marked by theend of the pulse 177. There is then another slanting portion to thepulse which is due to the discharge of condenser 182. It is the upwardlysloping portion of the pulse which is used for control purposes forcontrolling the energization of the winding of the braking motor 39 aswill be presently described.

The output of transistor 1%, as it appears across the resistor 1%, ispassed through a rectifier gate 197 to a condenser 264 which isconnected through a conductor 2% to the input of the lead network andamplifier 85. The rectifier gate 197 is normally nonconductive andbecomes conductive only upon the application to control terminalsthereof of a pulse voltage. The rectifier gate 197 consists of fourdiodes 199, 2%, 2ti1 and 202. The upper terminal of resistor 196 isconnected to the junction of diodes 199 and 202. The condenser 204-,which is connected to the input of the lead network and amplifier 85, isconnected to the junction of diodes 2M and 2&1. It will be noted thatthe output across resistor 196 cannot normally be passed through tocondenser 204 since any current tending to flow through diode 199 isblocked by diode 2G8. Similarly, the current cannot fiow through thelower two legs of the bridge due to the blocking action of diode 2&2. Bymeans presently described, rectifier gate 1% is periodically renderedconductive to permit the voltage pulses across resistor 196 to passthrough the rectifier gate 197. These voltage pulses when so passed areapplied to charge the condenser 204 which is connected to the outputterminal of the gate 197 between diodes 2% and 2d]. and ground conductor185.

Going over to the left hand side of the comparator 79, the output ofintegrator 70 is connected by a conductor 205 to the input terminal 206of the comparator 79. The voltage so applied consists of a series ofpositive pulses, illustrated as wave form 212, the leading edges ofwhich are spaced from each other by a distance equal to the spacingbetween the vertical synchronizing pulses. This vertical synchronizingsignal is applied through a resistor 207 and a blocking capacitor 209 toa blocking oscillator generally designated by the reference numeral 239.This blocking oscillator includes a transistor 211 of the NPN typehaving the usual base, emitter and collector. The emitter is connectedto conductor 18 leading to a source of negative potential so that uponapplication of a positive pulse to the base, the emitter becomesconductive. Transistor 211 is connected in series with the primarywinding 213 of a pulse transformer having the primary winding 213, afeedback winding 21d and an output winding 215. Upon transistor 2.11being rendered conductive by the application of the verticalsynchronizing pulse to the base of transistor 211, current flows througha resistor 216, the primary winding 213 and transistor 211 to theconductor 184 connected to the negative source of potential. The resultof this is that there is an abrupt flow of current through the winding213. This induces in the feedback winding 214 a voltage pulse, thepolarity of this pulse being positive as measured between the lower andupper ends, respectively, of winding 214. This positive pulse is appliedthrough conductor 217 and diode 213 to the base of transistor 211 tofurther increase the conductivity of the transistor 211. The result isthat the conductivity of transistor 211 rises rapidly to the saturationpoint. When this happens, current flow through primary winding 2T3ceases to increase with the result that the feedback voltage induced inwinding 214 drops to zero. This, in turn, results in the transistor Zilbeing cut oil. The back voltage that will be present at the collector oftransistor 211 when the field of the primary windin starts to collapsemay be so high as to cause damage to the transistor. Consequently, adiode 229 is connected across the primary winding 213 to prevent voltagebreakdown of the transistor 211.

The rapid buildup and then drop-off of the current through primary 213results in a pulse being induced in output winding 215. The Wind. 1215is so disposed with respect to primary winding all?! that during thepulse, the lower end of the secondary winding 2l5 is positive withrespect to the upper end. The winding 21 is connected across twoopposite terminals of the rectifier gate 197 through a networkconsisting of a resistor 222 and a condenser 223. This network isprovided for the purpose of providing a back bias for the rectitier gate197. The voltage built up across condenser 223 tends to maintain thelowermost terminal of rectifier gate negative with respect to theuppermost terminal during the periods between pulses. The resistor 22?;bypasses the condenser 223 to allow the voltage across condenser 223 toslowly leak oil. When the pulse appears across secondary winding 2.15,this pulse causes a current flow from the lower end of winding 215through a condenser 223, through diodes 291 land on the one hand, andthrough diodes 2532 and 1&9 on the other hand back through conductor 224to the upper terminal of secondary winding 215. The effect of this pulseis to create current flow through both sets of diodes which now act as avoltage divider, the potential at the junction of diodes 232 and 19?being the same as at the junction between diodes 26R and 209. If thepotential at the junction between diodes 262 and 199 is raised as aresult of a voltage across resistor 196, the potential at the oppositejunction, that is the junction between diodes 2432. and 2% iscorrespondingly raised so that it is now possible for any voltageappearing across resistor 1% to be transmitted to the condenser 204- forthe duration of the pulse. During this brief interval, condenser 204 ischarged.

The extent of the charge depends upon the relative position of the pulseacross winding 215 with respect to the trapezoidal voltage appearingacross resistor 196. The phase position of the trapezoidal voltage isdetermined by the point at which the pulse is produced by head 81 which,in turn, is determined by the speed of the drum. The apparatus isdesigned so that when the drum is rotating at the proper speed withrespect to the longitudinal speed of the tape as indicated by thevertical synchronizing pulses, the pulse appearing across secondarywinding 215' will occur somewhere along the upwardly sloping portion ofthe trapezoidal pulse. If the pulse across winding 21S occurs justbefore the peak of the trapezoid, a relatively large voltage will appearacross condenser 204. If, on the other hand, the pulse occurs near thelow point of the upward slope of the trapezoid, a relatively smallvoltage will appear across condenser 204. Condenser 2% is thus subjectto a series of pulses, the magnitude of which depends upon the relativephase position of the vertical synchronizing pulse and the pulse inducedin the head 81 by reason of rotation of the drum. The voltage acrosscondenser 2% is used to control the input to the lead network andamplifier to, in turn, control the energization of braking winding &3 ofthe braking motor 39.

The operation of unit will now be described. The voltage from condenser2% is applied through conductor 203 to the base of a PNP transistor 227.This transistor is in turn connected through a compound connection to asecond PNP trasistor 228, the emitter of transistor 227 being connectedto the base of transistor and the collectors of the two transistorsbeing connected together and to conductor 153 which, as previouslypointed out, leads to a source of negative potential. The emitter oftransistor 228 is connected to ground through a resistor 2%. Theemitter-collector voltage of transistor 228 is applied to the base of anNPN transistor 231 through a voltage divider network which functions toprovide an anti-hunting effect. This network consists of a firstresistor 23?. and a capacitor 233 connected in parallel with each otherbetween the emitter of transistor 22% and the base of transistor 231.Connected between the base of transistor 231 and conductor 184 leadingto the source of negative potential, is a second resistor 235 and asecond condenser 236. The resistance value of resistor 235 and thecapacitance of condenser 236 are relatively small as compared with theresistance value of resistor 232 and the capacitance of condenser 233.In one particular embodiment of my invention, I employed a 47 kilohmresistor 232 and a 5 microtarad capacitor 233. In this embodiment, theresistor 235 had a resistance value of 4.7 kilohms and the condenser 236a capacity of .25 microfarad. The two resistors 232 and 235 function asa voltage divider to apply a relatively small portion of theemitter-collector voltage of transistor 2.28 between the base andemitter of transistor 231, the emitter of transistor 231 being connectedto the power supply conductor 184 by a resistor 237.

The function of condenser 233 is to provide an antihunting effect, aspreviously mentioned. If the voltage across condenser 20 changes as aresult of the change in the relative speeds of the tape and the drumcarry .g the head 16, this change in voltage will pass more readilythrough the relatively large condenser 233 so as to cause a substantialincrease in the proportion of the output of transistor 223 which isapplied between the base and the emitter of transistor 231. Furthermore,this voltage, due to the phase shifting effect of capacitor 233, willtend to lead and cause the voltage to be applied to the base oftransistor 231 earlier than would otherwise be the case. The function ofcondenser 236 is to by-pass any extremely high frequency components dueto an erratic change in voltage.

Transistor 231 is in turn connected to a PNP transistor 240, thecollector of which is connected to ground and the emitter of which isconnected to the base of a further PNP transistor 241. The emittercollector path of transistor 241 is connected in series with winding 43so that a current may flow from the positive terminal of direct currentsource 46 through winding 43, the emitter and collector of 241 and toground, the current flow through this path depending upon theconductivity of the emitter collector path of transistor 241.

It will thus be seen that the current applied to winding 43 iscontrolled by the voltage on condenser 204 which, in turn, is dependentupon the relative phase relationship of the vertical synchronizing pulseand the pulse supplied by head 81 which produces the trapezoidal voltageat point 1912.

Referring now to the over-all operation of the cornparator circuit, ifthe drum 15 starts to speed up, the pulses 177 occurring at point 176will become more closely spaced to each other. This will in turn advancethe position of the trapezoidal voltage wave at point 192 causing thepulse appearing across the secondary winding 215 to occur at a laterpoint along the upwardly slopn'ig portion of the trapezoidal wave toproduce a larger voltage across condenser we to increase the voltage onthe base of transistor 227. Due to the various stages of amplificationin amplifier 85, this will result in transistor 241 becoming moreconductive to in turn cause more current to flow through braking winding43. This increases the braking effect of the braking motor 39 to in turnreduce the speed with which drum 15 is driven by motor 28 (shown inFTGURE 1). This will result in the pulses 77 at point 17:; becoming morewidely spaced apart 13 so as to retard the phase of the trapezoidalpulse at point 192. This in turn tends to increase the voltage appearingacross condenser 204 to, in turn, reduce the current flowing throughbraking winding 43. The apparatus stabilizes at a point Where the properphase relationship is maintained between the vertical synchronizingpulses representative of the longitudinal speed of the tape and thepulses produced in head 81 as a result of drum rotation.

The effect of condenser 233, as previously pointed out, is to provide ananti-hunting effect. Any change in the voltage across condenser 204 asthe result of the change in relative speeds of the drum and tape istransmitted through condenser 233 with a slight lead angle so that thebraking effect of winding 43 is changed slightly in advance thus tendingto anticipate the need for change in braking effect. The condenser 236,by passing high frequency changes in voltage, tends to prevent anyerratic effect that might occur as a result of high frequency voltagechanges introduced into the system.

When the apparatus is first started up, the pulses 177 will be spacedwidely apart due to the relatively slow speed of the drum. Thus when thepulse existing across winding 215 is applied to the rectifier gate, theprobability is that the voltage appearing at point 172 will be zerosince there will be no trapezoidal pulse present. At the same time, theamplitude of the trapezoidal wave will be relatively small since theamplitude of the pulse is dependent upon the speed with which the magnet89 passes the head 81. Thus, regardless of what is the phase displacement between the vertical synchronizing signal and the pulsesresulting from pulses produced in head 81, the average voltage impressedupon condenser 204 will be relatively small and hence, the brakingcurrent supplied to winding 43 will remain relatively small. In thisway, it is possible for the drum to come up to speed without beingunduly retarded by the braking motor 39.

As the apparatus approaches synchronization, the trapezoidal nature ofthe wave form appearing at point 192 will enable the synchronization tobe completed. While the two sets of pulses are still changing in phasewith respect to each other, it will be obvious that the voltage producedacross capacitor 204 will be relatively small since sometimes when thepulse existing across winding 215 is applied to the rectifier gate 197,the trapezoidal Wave will be at a low point in its cycle, that is, apoint between two successive trapezoids so that a zero voltage will beapplied to the condenser 264. At other times, the pulse may occur at apoint corresponding to a point on the slope or still at other times to apoint at the high point of the trapezoid. As a result the averagevoltage applied to condenser 204 will still be relatively small andhence the braking effect will likewise be relatively small.

Turning now to the case in which the drum and the vertical sync signalare substantially synchronized, the apparatus is so designed thatregardless of what will happen the correcting action will not stop untilthe desired relationship has been obtained, that is, until the pulseoccurring across winding 215 occurs at a point part way-up the upwardslope of the trapezoidal wave form. Let it be assumed that the pulseoccurs adjacent a downwardly sloping portion of any particulartrapezoidal wave. The resulting braking effect will tend to retard themovement of the drum which will move the pulse further up the downwardlysloping curve to in turn increase the braking effect still further. Bythe time that the pulse is adjacent the top of the trapezoid, thebraking effect will be at its maximum and the drum speed will slow downeven more until the gating pulse occurs adjacent the upwardly slopingportion of the trapezoidal wave. When this happens, any braking effecttends to decrease the voltage applied to condenser 204 which in turntends to decrease the braking effect to speed up the drum. Thus, it isonly when the voltage pulse is adjacent the upwardly rising portion ofthe trapezoidal voltage wave that the apparatus is stabilized.

With this arrangement, it is possible to vary closely control thesynchronization of the head position with the incoming video signal. Inone actual embodiment, the time represented by the upwardly slopingportion of the trapezoidal wave was 2.2 milliseconds. Thus a relativephase shift of the vertical synchronizing signal and the head signal ofas little as two milliseconds is prevented by this apparatus. This isvery desirable since it is highly important to the operation of theapparatus that the head 18 cross the edge of the tape at the same point,namely, at the end of one field of the video signal. When the headcrosses the gap between the two edges of the tape helically disposedabout the drum, it is inevitable that some portion of the signal will belost. As pointed out above, by insuring that the head always crosses thegap between the two edges of the tape at the time that one field isbeing completed prior to the time that a new field is started, verylittle of the actual picture is lost. It is true that the verticalsynchronizing signal is lost but as pointed out above, I have providedmeans for reinserting a vertical synchronizing signal into thereproduced video signal before it is applied to the video output means.The means for recording the audio signal is shown in substantially thesame way in FIGURE 3 as in FIGURE 1. The source of audio signal 39 isconnected through a record amplifier to the audio record head 20. Theoutput of the sound bias oscillator 91 is connected through the recordcontact of a changeover switch 243 and condenser 244 to the sound head29. The purpose of condenser 244 is to offer a relatively low impedanceto the output of the bias oscillator 91 and at the same time to blockthe passage of the relatively lower audio frequency to the erase head18. it will be noted that the sound bias oscillator is connecteddirectly through the switch $.43 to the erase head 18.

The other erase head 19, as previously pointed out, is connected to adirect current source 93. This connection is likewise through achangeover switch 245 which is shown in the record position in which themovable switch member is in engagement with a record contact M6. Withthe switch 245 in this position, the direct current source 93 isdirectly connected to the erase head 19.

DESCRIPTION OF FIGURE 4- FIGURE 4, like FIGURE 3, shows certain elementsin block diagram as they were shown in FIGURE 2. Certain other elements,however, which are shown in block diagram in FIGURE 2 for purposes ofsimplicity have been shown in circuit form in FIGURE 4- because of theimportance which they play in the operation of the apparatus and becauseof the fact that they have certain novel features of importance as faras the novelty of the present invention is concerned. As has been donepreviously, the same reference numerals are employed to designateelements corresponding to those which have previously been described inconnection with other figures.

As described in connection with FIGURE 2, the signal picked up by therecording and reproducing head 16 is passed through the couplingtransformer s4, and the changeover switch 58 to the primary winding 1%of the step-up transformer 161. A resistor 2-45 is connected across thesecondary winding 192 of the transformer 161. The purpose of thisresistance is to reduce the Q of the circuit and to reduce the effect ofthe resonant condition. The signal from transformer 1 12 is passedthrough the pro-amplifier M3 to the phase equalizer 1W- which will nowbe described.

The phase equalizer comprises a PNP transistor 247 having a base 243, anemitter 249, and a. collector 250. The emitter 249 is connected througha resistor 252 to -a conductor 253 leading to a suitable source ofpositive direct current voltage. In the particular embodiment of theapparatus with which I have been concerned, a source 15 of potential ofplus twelve volts was employed. The base 243 to which is connected theoutput of the pre-amplifier M33 is connected to the junction of tworesistors 253 and 2 54 which are connected between conductor 2525leading to the source of voltage and ground. These two resistors act asa voltage divider to normally maintain base 248 at a desired positivevoltage. The signal from the preamplifier IE3 is effective to vary thepotential of base with respect to emitter 249 to vary the conductivityof the transistor. Connected in series with the collector 25% is afurther resistor 255. The numeral 256 is used to designate the outputterminal of the phase equalizer 394. This terminal 256 is connected tothe emitter 2-69 by a resistor 257 and to the collector by a capacitor259. The condenser 259 acts as a variable impedance, its impedancedepending upon the frequency of the signal. For very high frequencysignals, its impedance is relatively low and point 256 is effectivelyconnected to the collector. For very low frequencies, the impedance ofcondenser 259 is very high so that the impedance of resistor 257 becomesrelatively low as compared with that of condenser 259 and point 256 iseffectively connected to the emitter 249. When point 256 is connected tothe emitter 24%, it is, in effect, connected to the positive side of thevoltage existing across the emitter collector path, when it is connectedto the collector 250, it is connected to the negative point of theemitter collector voltage. Thus, there tends to be a shift approaching180 degrees in the phase of the output voltage at terminal 256 dependingupon Whether it is connected to the emitter r collector. As pointed outabove, the effective point of connection depends upon the capacitance ofcondenser 259 which, in turn, depends upon the frequency of the signalbeing transmitted. The net effect is that the phase equalizer itl icauses the phase to be retarded as the frequency increases. It has beenfound that there is some tendency in a system of this type for the phaseto lead as the frequency of the signals increases. The phase equalizer1G4 compensates for this shift in phase which would otherwise occur dueto changes in frequency of the signal.

From junction point 256, the signal is supplied to the video amplifierTilfrom which it passes into the clamp and blanking unit 1% which willnow be described.

The output of the video amplifier 105 first passes through a condenser26?. where it is applied to the base of an NPN transistor 263.interposed between the base of transistor 263 and ground is a clampingdiode 264 which cooperates with the condenser 262 to insure that thetips of the synchronizing pulses do not fall below ground potential. Thecollector of transistor 263 is connected to conductor 265 leading to asuitable source of positive potential, for example, plus twelve volts.The emitter of transistor 263 is connected through an emitter followerresistor 266 to a conductor 267 leading to a suitable source of negativepotential, for example, minus twelve volts. The output of transistor 263appearing across the resistor 266 is a video signal in which the tips ofthe synchronizing pulses have been clamped to have a uniform height.

The voltage across resistor 266 is applied to the base of anothertransistor 27d, the emitter of which is con nected through a resistor271 to the conductor 267 leading to the negative source of potential.Similarly, the collector of this transistor 27% is connected toconductor 265 which is maintained at a positive otential. The voltageacross resistor 271 is connected through a condenser 272 and conductor273 to the video output device 167. Before being applied, however, tothe video output device, it is subjected to the action of variousclamping circuits. In the first place, lprovide a clamping means forperiodically clamping the video output signal to insure that thepotential of the pedcstal is at zero. This clamp means will now bedescribed.

The output of the transistor appearing across rcsistor 266 is not onlysupplied to the base of transistor 270 but is also connected through aconductor 280 to the input of a sync stripper 281 for extracting thehorizontal synchronizing pulses from the video signal. The output of thesync stripper 281 is passed through a one-shot multivibrator 282 toproduce a series of square-wave pulses, one for each horizontalsynchronizing pulse. Each such pulse is initiated at the end of thehorizontal synchronizing pulse or at the back porch of the pedestal ofthe synchronizing pulse. The output of the one-shot multivibrator 282 isthen passed through a condenser 283 and a pulse shaping networkconsisting of a condenser 285 and a resistor 286. The resultant pulsesare applied to the base of an NPN transistor 289, the collector of whichis connected through a resistor 276 to conductor 265 connected to apositive source of potential and to the cathode of a diode 275. Theemitter of transistor 289 is connected to ground at 290. The base islikewise connected to ground by a resistor 2%. It will be readily seenthat the emitter collector path of transistor 289 connected in serieswith diode 275 so that there is a path for the video signal, when thetransistor 289 is fully conductive, through the diode 275', thecollector and emitter of transistor 289 to ground. The horizontalsynchronizing pulses, as modified by the one-shot multivibrator 282 inthe pulse shaping network consisting of condenser 285 and resistor 286,are effective each time that one of these pulses is applied to the baseof transistor 289 to render the collector emitter path conductive. Whenthis happens, the video output signal is clamped to ground. The phasingof the system is such, as pointed out above, that this occurs during theback porch portion of the signal so that the pedestal level is clampedto ground potential.

I also provide means for clamping the tips of the synchronizing pulsesto a slightly negative voltage such as minus one volt. Connected betweena conductor 297 leading to a suitable source of negative potential, suchfor example as minus twelve volts, and ground are three resistors 298,2%, and 393. These three resistors act as a voltage divider beingconnected at one end to the negative conductor at minus twelve volts andat the other end to ground. The value of the resistors is so chosen thatthe junction of resistors 29% and 299 is at a potential of minus 2 /2volts in the example mentioned, and the junction of resistors 299 and300 is at a voltage of minus one, both voltages being approximate.Condenser 295 is connected across resistor 300 and condenser 2% acrossresistors 299 and 300 to by-pass any high frequency voltage componentsthat might be present in the voltage applied across resistors 298, 299,and 390. The junction of resistors 299 and 3% is connected through aconductor 301, diode 302, and conductors 303, 304, and 273 to the videooutput 107. The diode 302 acts in conjunction with condenser 272 toprovide a clamping effect in that the tips of the synchronizing pulsescan never go below the potential between the junction of resistor 299and 300, which in the example given is approximately minus one volt.

It will thus be seen that as a result of the combined action of the twoclamping means described that the peaks of the synchronizing pulses arealways clamped, in the example mentioned, to minus one volt so that theycannot exceed that potential in the negative direction. This is becauseof the clamping connection provided by diode 302. Due to the action ofthe clamping action provided by diode 2'75 and transistor 239, thesignal is further clamped at the pedestal level to ground potential. Thelatter clamping action occurs at the beginning of each trace just as thesignal passes through the back porch portion of the signal. Because ofthis dual clamping action occurring at the end of each horizontal trace,any low frequency components which may have been lost due to therecording limitations of the head at the relatively low recording speedsat which my apparatus operates, are recovered. Because of the fact thatsuch low speed signal variations are rccovered in this manner, it ispossible in my apparatus to employ straight recording of the videosignal as distinguished from the use of the signal to frequency modulatea high frequency voltage as is done in many systems of this typeemploying relatively low recording and reproducing speeds.

It was also noted above that I have provided means for restoring thevertical synchronizing signal that is lost at the end of each field whenthe head 16 is passing over the gap between the two edges of the tape.The means for doing this will now be described.

The head 81 associated with the magnet 80 for measuring drum speed has,as previously pointed out, a pulse produced therein for each revolutionof the drum. This series of pulses is applied to the amplifier 82 andfrom there to the one-shot multivibrator 175 as described in connectionwith FIGURE 3. The output of this one-shot multivibrator is supplied tothe clamp and blanking unit 106, being passed through a pulse shapingnetwork consisting of a resistor 305 and a condenser 306. The output ofthe pulse shaping network is passed through a blocking condenser 307 tothe base of an NPN transistor 310, the base of which is furtherconnected to the emitter by a resistor 311. The collector of transistor310 is connected through a resistor 312 and a conductor 313 to theconductor 265 leading to a positive source of potential. This transistorserves to periodically clamp the video signal being supplied to thevideo output 1tl7 to a voltage value such that no video signal can pass.

It will be noted that a circuit can be traced from the video output 107through conductors 273, 334, a diode 315, the collector and emitter oftransistor 310 and conductor 316 to the junction of resistors 298 and299 of the voltage divider. This junction, as previously pointed out, isat a potential of approximately minus 2 volts. When the transisor 310 isrendered conductive as the result of the pulse being applied from head31 through the amplifier 32 and the multivibrator 175, the video outputis effectively connected to this junction between resistors 298 and 299.In actual practice, the potential to which the video output is connectedis substantially higher than minus 2 /2 volts due to the voltage dropsthrough the diode 315 and the transistor 31% Thus, at the time thetransistor 310 is rendered conductive, the video output is actuallyreduced to a potential of approximately minus one volt, which is thesame as that to which the tips of the horizontal synchronous pulses wereclamped, due to the connection from the junction of resistors 299 and300 through diode 392 to the video output.

As a result of transistor 310 periodically being rendered conductive andthe video output being clamped to a voltage of approximately minus onevolt, the entire video signal is brought into the black range whichstarts at approximately zero volts. At this stage in the apparatus, thenormal video signal is positive. Hence, no picture information istransmitted to the video output device at the time that transistor 310is conductive. Taere are several purposes to this. In the first place,as has been pointed out previously, the signal along the edges of thetape was erased during the recording operation and the audio signalrecorded along one edge and the synchronizing control signal along theother edge. These two signals, if scanned by the main head 16 andtransmitted through to the video output 107, would create a disturbingeffect since they have no significance as far as the picture informationis concerned. By blanking out the signal to the video output at a timecorresponding to the time when the head passes the edges of the tape, itis assured that any signal picked up by the head when it passes theedges of the tape will not be transmitted to the video output. At thesame time, a sudden change in the signal supply to the video output dueto the signal being suddenly moved to a potential of minus one volt inthe black range creates a pulse in the signal supplied to the videooutput, which pulse is properly timed and of a character to act as avertical synchronizing pulse. The one-shot multivibator 175 is designedto produce a pulse which is of a different order of magnitude than thehorizontal synchronizing pulse. A typical horizontal synchronizing pulsehas a duration of only a few microseconds, whereas the pulse supplied bythe multivibrator 175 has a length of about 2.6 milliseconds. This pulseis comparable in length to the typical vertical synchronizing pulse sothat as far as the video output apparatus is concerned, the reduction ofthe video output signal to the minus one volt value for this period oftime creates an elfect similar to that of a typical verticalsynchronizing signal. In this way, with my apparatus, the verticalsynchronizing signal which must of necessity be lost in the recordingoperation, is effectively replaced.

The means for controlling the speed of the drum 15 will now bediscussed. As pointed out in connection with FIGURE 2, the signal fromthe head 21 which reproduces the control signal recorded along one edgeof the tape is amplified by an amplifier 113 and compared with thesignal from the head 81 to control the operation of the braking motor 39to maintain a drum speed at a desired value with respect to the tapespeed. The operation of the comparator 79, the lead network andamplifier S5, and the braking motor 39 are exactly the same as duringthe recording operation and need not again be described. The means,however, for amplifying the signal from head 21 will, however, bediscussed.

The signal from head 21 first passes through switch 169 which is now inthe playback position so that switch 170 is in contact with the playbackcontact 171. From contact 171, the signal passes through a blockingcondenser 320 to the input of amplifier 113. The amplifier 113 has threePNP transistors 321, 322, and 323, each having the usual base, emitterand collector. The collectors are all connected to a conductor 325leading to a suitable source of negative potential, for example, minustwelve volts, Connected between the collector of transistor 321 andconductor 325 is a resistance 326. Similar resistors 327 and 328 areconnected between the collectors of transistors 322 and 323,respectively and conductor 325. A resistor 329 and a condenser 330 areconnected between the base and the collector of transistor 321. Thecondenser 330 is provided for limiting the high frequency response ofthe amplifier to reduce the effect of extraneous high frequencydisturbances. The output of transistor 321 is connected through ablocking condenser 331 to the base of the second transistor 322. Aresistor 332 and a condenser 334 are connected between the base oftransistor 322 and its collector. The function of condenser 334 issimilar to that of condenser 330, namely to limit the response of theamplifier to extraneous high frequency disturbances. The output oftransistor 322 is connected through a condenser 336 to the base of afinal transistor 323. The emitters of all three transistors 321, 322,and 323 are connected to a ground conductor 337, connected to ground at338. The connection of the emitter of transistor 321 to ground includesa resistor 339 to reduce the gain at that stage.

interposed between the base of the last transistor 323 and groundconductor 337 are a resistor 340 and a diode 341. The diode 341 isprovided for the purpose of clamping the input of the base to ground toinsure that the signal supply to the base of transistor 323 cannot useabbve ground potential. In this way, it is assured that the signalsupplied to transistor 323 will always be below ground potential andthat the pulses supplied to the base of that transistor will besufficiently negative to drive the transistor to saturation.

The output of transistor 323, which constitutes the output of amplifier113, is then supplied to the comparator 79 where it is compared with thesignal from the oneshot multivibrator which, in turn, is dependent uponthe signal generated by head 81. As has been described in connectionwith both FIGURES 2 and 3, the pulse from the head 81, dependent uponthe speed of the rota- 19 tion of drum 15, is compared with the signalfrom the output of amplifier 113 which is dependent upon the speed ofthe tape. The output of the comparator then passes through a leadnetwork and amplifier 85 to control the energization of winding 43 tocontrol the braking effect of winding 39. As has been described indetail in connection with FIGURE 3, this is then employed to maintainthe relative speeds of the drum .15 and the motor 23 (shown in FIGURE 1)driving the tape at such a value that the head 16 will always pass theedges of the tape at the end of a video field.

As has been also pointed out previously, it will be noted that thesignal produced in head 81 by rotation of the drum is used for threedistinct purposes, one, to blank out the video output signal to removeany effects of the audio signal and the control signal from the videosignal. The next effect is to insert in the video output signal a pulsewhich is capable of being employed as a vertical synchronizing signal.Lastly, the same pulse produced by head 81 is employed to control thespeed with which the head is driven with respect to the longitudinalspeed of the tape.

The apparatus for reproducing the sound is shown in the same manner asin FIGURE 2 and need not be repeated here. The output of the head 29 isconnected through amplifier 108 to the audio output device 109. It willbe noted that the two erase heads 18 and 19 are effectively disconnectedsince changeover switches 243 and 245 are in their playback positions inwhich the movable switch contact of each of these switches is inengagement with a playback contact which is effectively dead. It isobvious that no erasing action is desired during the reproducing orplayback portion of the opera tion.

In the foregoing description, reference has been made only occasionallyto the values of the components. It is to be understood that thesecomponents may have various values within the scope of the invention. Inone particular embodiment of the invention, the following componentswere employed. In this same embodiment, the voltages employed were thosewhich have been referred to above. It is to be understood that thevalues and components named are illustrative only and that the scope ofthe invention is not to be construed as limited to the values orparticular components named.

Transistors:

115 2N1309 116 2N1308 155 2N1304 179, 190 2N1305 211 2N1304 227, 2282N1305 231 2N1304 240 2N1305 241 2N301 247 2N1309 263, 270 2N2712 289,310 21J1304 321, 322, 323 2N1305 Inductors:

141 millihenries 146 microhenries 10 Diodes:

164, 186 IN270 199, 260, 201, 202, 218 and 22 0 IN458A 264, 275 IN3067302, 315, 341 1N270 Condensers:

129 microfarads 20 139 -picofarads 72 147 do 6068 166 microfarads 5 182,204 rnicrofarad- .25 209 picofarads 4700 223 microfarad 1 2.0Condensers:

233 microfarads 5 236 microiarad .25 25? picofarads 200 262 microfarad.01 272 do .05 283 do .1 235 ieofarads 270 295 microfarad 1 296 do 1 305picofarads 270 397 microfarads 5 320, 331 do 10 33%, 334 picofarads 200336 microfarads 5 Resistors:

128 kilohms 10 my, 133 ohms 39 137 kilohms 1.5 133 ohms 470 140 do 82015G kilohm 1 159 kilohms 1.5 161 ohms 47 163 kilohms 47 133, 196 kilohm1 207 l ilohms 12 216 ohms 22 222 kilohms 330 230 do 2.7 232 d0 47 235do 4.7 237 ohms 390 245 kilohms 10 252 ohms 270 253 kilohms 4.7 254 do15 255 ohms 390 257 kilohms 1.5 266, 271, 275 do 2.2 286 do 4.7 291 lilohm 1 298 ohms 330 299 do 82 3% do 33 3116 kilohms 4.7 311 kilohm 1312 lrilohms 2.2 326 do 10 327 kilohm 1 328 kilohn1s 2.2 329 megohm 1332 kilohms 1G0 339 ohms 340 kilohms 47 DESCRIPTION OF FIGURES 5, 6 AND7 In the foregoing description, the drum 15 has been merely described ascontaining a head 16 and a coupling transformer 64. In actual practice,I have found it desirable to provide certain expedients to bring thetape into better contact with the head 16. In order to show this, I haveshown certain details of the drum in FI URES 5, 6 and 7, which detailsare not shown in the schematic FIGURES l to 4.

In the first place, the head 16 is mounted on an insert plate 350 whichmay be held in position in the drum by a plurality of fastening means351, such as screws. Extending closely adjacent to t1 e head 16 are twoslots 353 and 354. These slots extend very closely to the head andextend past it in both directions into the main body of the drum. Theslots moreover vary both in depth and width. At their maximum depth,adjacent the center of head 15, these slots are .020 inch in depth. Theytaper in both directions to a zero width and depth.

The slots 353 and 354- are provided for the purpose of bringing the tapeinto closer engagement with the head 16. In order to prevent wear on thetape, the head is substantially flush with the surface of the drum,projecting only one thousandth of an inch or so from the surface of thedrum. Since the drum revolves at a relatively high speed, producing anair cushion between the tape and the drum, there is some tendency forthe tape to be separated from the drum. This, of course, tends to impairboth the recording and reproducing functions. The slots 353 and 35a tendto bring the tape into closer contact with the head 16 since these slotscreate a depression on either side of the head 16. By providing theseslots, it is accordingly possible to have the head project much lessfrom the surface of the drum than would otherwise be the case.

Considering now the recording system of FIGURE 8, the alternateembodiment thereof differs in several respects from that of FIGURE 3. Inthe embodiment of FIGURE 8, video signal source 58 applies video signalsvia a resistor ass and a coupling capacitor 353 to an amplifierpro-emphasis stage sea and a synchronizing stripper and amplifier 362.The synchronizing stripper and amplifier 362 strips synchronizingsignals from the video signals and amplifies the signals to a desiredlevel. T hereafter, the amplified synchronizing signals are applied viaa resistor 2554 and the coupling capacitor 353 to the amplifierpro-emphasis stage 386.

The amplifier pre-emphasis stage 36% comprises a video amplifier,including two transistors 36d and 3'53, and a preemphasis network 37%.The video amplifier further includes resistors 37?) and 3Y4 whichestablish an operating level for transistor 366. The collector oftransistor 356 is connected via a load resistor 376 to a source ofnegative potential 378, for example -18 volts, and the emitter isconnected to a ground conductor 3$t3 through pie-emphasis network 37%.Pro-emphasis network 370 includes two inductors 382 and 33-6 and acapacitor 336 connected in series circuit relationship. Additionally asecond capacitor 388 is connected in parallel with inductor 382 and asecond resistor 398 is connected in series with the capacitor 383 and inparallel with inductor 334. The collector of transistor 366 is connecteddirectly to the base of transistor 368. The emitter of transistor 368 isconnected to the source of negative potential 3'78 while the collectorthereof is connected to ground conductor 38% via resistor 395:. Anegative feedback circuit is provided between the collector oftransistor 368 and the emitter of transistor 366. This negative feedbackcircuit includes a coupling capacitor and the transducing head 16 whichis operatively connected in parallel to capacitor 395; via the bias trap53.

The amount of negative feedback from transistor 368 to transistor 366 isa function of the impedance of the pro-emphasis network 37%) whichvaries in response to the frequency of the video signals. At relativelylow frequencies, the negative feedback circuit impedance is relativelylow resulting in relatively little feedback such that relatively highlevel recording signals are applied to the transducing head 16. Atintermedate frequencies, the negative feedback circuit impedanceincreases relative to its impedance at low frequencies resulting inincreased negative feedback such that lower level recording signals areapplied to the transducing head 16. At the higher frequencies, thenegative feedback circuit impedance increases substantially compared toits impedance at either low or intermediate frequencies such that thelow level recording signals are applied to the transducing head 15.

The amplified and pre-emphasizcd video signals are superimposed upon andadded to a video biasing signal produced by the video bias oscillator54. Bias trap 53 prevents the video biasing signals from passing intothe am plifier preemphasis stage see. The video signals, in the form ofrecording signals, are applied via conductors 402 and 4M and transformer64, to transducing head 16.

22 Dashed line 406 illustrates an electrical connection betweenconductors 402 and 40d and primary winding 63 of transformer 64;, whichtransformer at supplies recording signals via secondary winding 65 totransducing head 16.

Referring now to the electrical circuitry for controlling the speed ofthe head 16, the synchronizing stripper and amplifier 362 also appliesamplified synchronizing signals to the integrator 70. integrator 76applies a control signal derived from the vertical synchronizing signalto a sync head driver 4% and to a comparator 414. Sync head driver 408illustrated in block form includes the sync pulse amplifier 73 and synchead driver 74 of FIGURE 3. Sync head driver 408 produces and applies anamplified synchronizing signal or control signal to synchronizing head21. Head 21 records the control signal on one edge of the recordingmedium or tape 17.

In addition to the control signal from integrator 70, comparator 414receives a head position pulse from head 81 via amplifier 82 in the samemanner as described in FIGURE 3. The operational features of thecomparator 414 of FIGURE 8 differs from comparator 79 of FIG- URE 3 intwo important ways. The control signals applied to comparator 414comprise an input signal to a ramp generator circuit designated as 416which produces a sawtooth wave or series of spaced varying voltagepulses the amplitude of each of which steadily changes during at least aportion of the pulse duration. The head position pulses applied tocomparator 414 comprise an input signal to a blocking oscillator circuitdesignated generally as 418. The phase relation between the controlsignal and head position pulse is determined by a diode gate 420.

Considering the schematic diagram of the comparator 414, the rampgenerator circuit 416 includes PNP transistors 42.2 and 424. The controlsignals derived from the high frequency or video signals are receivedfrom integrator 7t! and applied via a coupling capacitor 423 to the baseof transistor 422. A resistor 432, connected between the base oftransistor 422 and ground conductor 43 i, estabiishes the operatinglevel of transistor 422 such that in the absence of a control signaltransistor 422 is nonconductive. The emitter of transistor 422 isconnected directly to the ground conductor 434. The collector oftransistor 422 is connected via resistor 436 and resistor 438 to asource of negative potential 449. Additionally the emitter of transistor422 is connected to ground conductor 434 via capacitors 446 and 443 andto the base of transistor 424. The emitter of transistor 2-24 isconnected via a resistor 45% to a common junction terminal between thecapacitors 446 and MS. The collector of transistor 424 is connecteddirectly to a source of negative potential Mill. Since the base oftransistor 424 is connected directly to the collector of transistor 422,transistor 42-1 will be conductive when transistor .22 is nonconductivedue to the negative potential which is applied to the base thereof fromthe source of negative potential 440. An output conductor 452 from theramp generator 416, which conductor 452 is connected to the emitter oftransistor 424, applies the varying voltage pulses to diode gate 421 Afilter capacitor 454 is connected between the common junction terminalof resistors 436 and 438 and the input to diode gate 420, which input isconnected to ground conductor 434 via a resistor 456.

Prior to integrator 7t applying the control signal to the base oftransistor 422, transistor 422 is nonconductive and transistor 424 isconductive. Capacitors 446 and 448 are charged via resistors 436 and 438from the negative source of potential Mill. When a control signal isapplied to the base of transistor 422, transistor 422 immediatelybecomes conductive to abruptly discharge capacitor 446 through its lowimpedance collector-emitter junction to ground conductor 434. As thepotential applied to the base and emitter of transistor 424 becomes lessnegative, transistor 424 becomes nonconductive but at a rate such thatthe discharge curve of the capacitors 446 and 448 is linearizedresulting in a sawtooth wave having a linear ramp portion. At the end ofthe control signal, transistor 422 is again rendered nonconductive whiletransistor 42% is rendered conductive. Capacitors 4% and 448 arerecharged by the source of negative potential 443. The resultant varyingvoltage pulses applied to the diode gate 420 are illustrated as waveform558.

Considering now the blocking oscillator 4-13, the oscillator includes atransistor 46?. which is adapted to receive a head position pulse fromamplifier 82 via a coupling capacitor 464. The transistor 462 isoperaiively coupled to a feedback transformer 456, which transformerincludes a primary winding 468, having a center tap 470, and a secondarywinding 4-72,. One end of the primary winding $68 is connected via aresistor 4-74 to the source of negative potential 446 while the otherend of winding 468 is connected via a resistor 4'76 to the base oftransistor 462. The emitter of transistor 462 is con nected to thecenter tap 470 and the collector of transistor 462 is connected directlyto the ground conductor 434. A bypass capacitor 473 is connected betweenresistor 474- and ground conductor 43%. Secondary win-ling 472 isconnected across diode gate 42s with a coupling network 484) connectedbetween one end of the secondary winding 472 and the gate 4-20. A diode482 is connected across the secondary winding 472 to minimize transientvoltages produced by the inductance of the transformer 46% duringswitching of transistor 562.

The head position pulse produced by head 31 is amplified by amplifier 82and applied via capacitor 464 to the base of transistor 462. Transistor462 is driven into conduction by each head position pulse to produce auniform voltage across secondary winding 472 due to current throughprimary winding 458 when transistor 4-62 is conductive. Thus, theblocking oscillator 413 is responsive to a series of head positionpulses to produce a series of spaced uniform voltage pulses theamplitude of each of which remains substantially constant during atleast a portion of the pulse duration. Tl e uniform pulses are appliedto the diode gate 426 via the coupling network ass. The output from theblocking oscillator 413 is illustrated as waveform 48 The pulses fromthe ramp generator 416 and the blocking oscillator 418 are applied todiode gate 420 of the comparator 414. Diode gate 426 produces aresultant signal or voltage signal the magnitude of which is dependenton the phase relation between the voltage pulses. The operation of diodegate 42% is similar to that of diode gate 197 as described in FIGURE 3and the operation thereof need not be repeated. The output from diodegate 42% is applied to a lead network and amplifier 496. The voltagesignal produced by the diode gate 420 is applied to the lead network andamplifier 499 via conductor 494 and the voltage signal is stored withina capacitor 492.

Considering now the operation of the lead network and amplifier 4%,transistors 496 and 498 function to amplify the voltage signal appliedto capacitor 492 and the base of transistor 4%. The other transistors506, 5-92 and 504 operate as a stable, linear D.C. amplifier having anegative feedback loop for stability. The DC. amplifier portion of thelead network and amplifier 4-90 produces a braking signal which isapplied to a power trai sistor 508. The power transistor 508 produces abraking voltage from the source of negative potential sea which controlsthe grounded braking winding 43 to regulate the speed of rotor 42 ofbraking motor 39 and subsequently the speed of rotation of head 16. Thebraking voltage is continually applied to braking winding 43 by the leadnetwork and amplifier 4% to keep the speed of rotation of head 16 insynchronism with the oblique tracks across the recording medium 17.

FIGURE 9 is an alternate embodiment of a reproducing or playback systemwherein the low frequency component and the erased verticalsynchronizing signal are replaced by various clamping circuits. Therecorded video signals are contained Within oblique tracks locatedbetween two spaced tracks recorded one on each longitudinal edge of therecording medium. The recorded video signals are reproduced from theoblique tracks by transducing head 16. Transducing head 16 applies thereproduced video signals through transformers 64 and 514 to a videoamplifier 5%. The video amplifier 536 amplifies and applies thereproduced signal to a clamp and blanking unit 529. The clamp andblanking unit 52% applies a composite video signal, having appropriatesynchronizing and blanking signals, to a video output device 522.

The clamp and blanking unit 52%, during reproduction of the videosignal, is controlled by a synchronizing signal stripper 524. Thesynchronizing stripper 524 functions to remove horizontal synchronizingsignals from the video signal received from video amplifier 51%.Additionally, the synchronizing signal stripper 524 controls operationof a back porch monostable multivibrator 526 in response to the trailingedge of the horizontal synchronizing sig- The function of multivibrator52-6 is to fix the back porch duration or the time interval between thetrailing edge of the horizontal synchronizing signal and the trailingedge of the horizontal blanking signal.

The clamp and blanking unit 52%, during the interval when head 16crosses over the recording medium edges, accomplishes vertical blankingand synchronizing under control of a vertical synchronizing signalmonostable multivibrator 528 and a vertical blanking signal monostablemultivibrator 539.

During playback, the position of the transducing head 15 is determinedby head 81 in response to magnet in a manner similar to that of theplayback system of FIGURE 4. However, in this embodiment, a second heador clamp pulse head 536 is disposed a predetermined angular distancefrom the first head 81, which in this embodiment is 186 to place thesecond head in radial alignment with the first head. Both heads 80 and536 are responsive to magnet 81 being passed thereby and the timeinterval between pulses is a function of the speed of rotation of head16. The angular displacement distance of clamp pulse head 536 isdependent on the timing required between the vertical blanking signal,the Vertical synchronizing signal and the time required for transducinghead 16 to cross the longitudinal edge of the tape containing therecorded synchronizing signals and audio signals. The reproduced videosignal supplied to the video output device 522 contains the appropriatesynchronizing and blanking signals.

Considering the schematic diagram of the clamp and blanking unit 520, acoupling capacitor 549 is connected between the video amplifier 516 anda resistor-diode clamping matrix. The capacitor 540 is connected to oneend of a resistor 542, the other end of resistor 542 being connected tothe anode of a diode 544. The cathode of diode 544 is electricallyconnected via a resistor 546 to a source of negative potential 559, forexample a negative 18 volts. A capacitor 548 connects the commonjunction terminal between the cathode of diode 544 and resistor 546 tothe vertical synchronizing monostable multivibrator 53%.

The end of resistor 542 connected to diode 544 is also electricallyconnected to the anode of a second diode 522. The cathode of diode 552is connected to the multivibrator 526. A resistor 554 is connectedbetween the source of negative potential 550 and the anode of diode 544in parallel with diode 544 and resistor 546. A third diode 556 has itscathode connected to the common junction terminal between resistor 55the anode of diode 544 and resistor 5'42 and the anode of diode 556 iscon nected to the multivibrator 526.

A pair of transistors 558 and 56th are connected in 2. Burlingtonamplifier arrangement with the base of transistor 553 being electricallyconnected to the common junction terminal between the cathode of diode556, resistor 554, the anode of diode 544 and resistor 54-2. Thecollector of transistor 558 is electrically connected to a groundconductor 562 via a resistor 564 while the emitter of transistor 558 isconnected to the base of second transistor 560 of the Darlington pair.The emitter of transistor 56!) is electrically connected to the sourceof negative potential 550 via resistors 566 and 568. The collector oftransistor 560 is connected directly to the ground conductor 562. Alsothe emitter of transistor 560 is connected via a capacitor 572 to thecollector of transistor 558.

A transistor 574 connected as an emitter follower has its baseconnected. to the common junction terminal between resistors 566 and 568while the collector thereof is directly connected to the source ofnegative potential 550. The emitter of transistor 574 is electricallyconnected to the ground conductor 562 via a resistor 576. A resistor 573operatively couples an output conductor 58b to the emitter of transistor574. Conductor S6 applies the resulting composite video signal to thevideo output device 522.

An output conductor 586 connects the clamp and blanking unit 52b to thesynchronizing signal stripper 524. The synchronizing signal stripper 524comprises a single transistor 5%, the base of which is connected toconductor 556 via resistor 590. The collector of transistor 588 iselectrically connected to the source of negative potential 550 via aresistor 592. The collector of transistor 538 is also connected via acapacitor 596 to a voltage dividing network comprising resistors 598 and600. The synchronizing signal stripper 524 has an output conductor 692electrically connected between the emitter thereof and the back porchmonostable multivibrator 526.

The multivibrator526 comprises two transistors 604 and 666. The base oftransistor 664 is electrically connected to the synchronizing signalstripper 524 at the common junction terminal between resistors 593 anddill). The emitter of transistor 604 is electrically connected throughresistors 608 and 616 to the source of negative potential 559. Theemitter of transistor 538 of the synchronizing signal stripper 524 iselectrically connected via conductor 662 to the common junction terminalbetween resistors 608 and 610. The collector of transistor 6% isconnected to ground conductor 562 via a resistor 612. The resistors 598and 660 of the synchronizing signal stripper 524 establish the operatinglevel of transistor 604. In the absence of a pulse from thesynchronizing signal stripper 524, the transistor 6% is normallyconductive due to the potential impressed upon the base thereof by thevoltage dividing resistors 5% and 600. Resultantly, transistor 606 willnormally be nonconductive. Conversely, when transistor 6% is renderednonconductive due to a negative going pulse, transistor 606 immediatelybecomes conductive. As will be described, when transistor 664 isconductive, the potential at the emitter of transistor 694 will beutilized to clamp the video signal at the black level. Conversely, whentransistor 666 is conductive, the voltage across resistor 611} or thepotential at the common junction of resistors 603 and 619 will beutilized to clamp the video signal at the blacker-than-black level. Aconductor 614 is also connected to the common junction terminal betweenresistors 668 and 616 and applies the voltage appearing thereacross tothe anode of diode 556 in the clamp and blanking unit 520.

The emitter of transistor 604 is also connected via conductor 616 to theemitter of the second transistor 6436 while the base of transistor 6% iselectrically connected to a common junction terminal between voltagedividing resistors 620 and 622. A capacitor 618 is connected between thesame common junction terminal and the collector of transistor 694. Thevoltage dividing resistors 62d and 622 extend between the source ofnegative potential 550 and ground conductor 562 and establish theoperating level of transistor 696. A capacitor 624 connects the emitterof transistor 696 to conductor 614. The collector of transistor 606 iselectrically connected to ground conductor 562 via resistor 626. Acapacitor 628 is electrically connected between conductor 61 i andground conductor 562.

The multivibrators 528 and 530 are conventional monostablemultivibrators utilizing diode steering and collector switching. Thus,the multivibrators 528 and 530 are illustrated schematically but theelectrical connections thereof need not be recited in detail since theelectrical connections and operations thereof are well known in the art.

The operation of the clamp and blanking unit 520 during a vertical fieldor half frame will now be considered. In one embodiment, the black levelfor the video signal was about -11 volts and the blacker-than-blacklevel was about l3 volts. Thus, the picture information was representedby voltages more positive than 11 volts up to about 6 volts.

The transducer head 16 reproduces the recorded video signals havinghorizontal synchronizing and blanking signals from the oblique tracks ofthe recording medium 17 and applies the same to the video amplifier5116. Ampliiier 516 applies the amplified reproduced video signals tothe clamp and blanking unit 520. The cathode of diode 544 iselectrically connected to ground via capacitor 548 and multivibrator 530while the cathode of diode 552 is electrically connected to groundconductor 562 via resistor 626.

The amplified reproduced video signals are applied to the base oftransistor 553 via capacitor 540. Since the cathodes of diodes 544 and552 are connected to ground, the video signals, which are more negativethan ground potential, back bias diodes 544- and 5512. Transistors 558and 56%) amplify and apply the video signals via transistor 574,resistor 57S and conductor 584} to the video output device 522.

However, the anode of diode 556 is electrically connected via conductor614 to the common junction terminal between resistor 608 and resistor610. Since transistor 604 is normally conductive and transistor 6% isnormally nonconductive, the anode of diode 556 is biased at thepotential of the common junction terminal between resistors 66% and 610.The potential at this common junction terminal is selected to be theblacker-than-black level. Thus diode 556, being biased at theblacker-than-black level, permits all the video signals to be passedexcept that diode 556 clamps the horizontal synchronizing signal tip atthe blackenthan-black level.

When the horizontal blanking and synchronizing signal portion of thevideo signals are applied to the Darling ton pair 558 and 560, thetransi.:tors S and 56d become non-conductive and transistor 58% of thesynchronizing signal stripper 524 is driven into conduction. Capacitor596 differentiates the leading and trailing edge of the horizontalsynchronizing signal. The negative going portion, or trailing edge, ofthe horizontal synchronizing pulse drives transistor GM of themultivibrator 526 into cut-oil or nonconduction. Immediately transistor606 of the monostable multivibrator 526 becomes conductive and remainsin its unstable state for a time period equal to the RC time constant ofresistor 622 and capacitor 613. This time period is equal to about 3microseconds or the back porch period. The back porch clamping timeperiod is meant to be the time interval of the horizontal blankingsignal between the trailing edge of the horizontal synchronizing signaland the trailing edge of the horizontal blanking signal.

When transistor 604 is conductive, the current through resistors 6%,616} and 612 and the emitter-collector junction of transistor 64%produces a predetermined voltage drop across resistor 698. in thisembodiment, the resistance of resistor 626 is selected to be equal tothat of resistor 612. Therefore, when transistor 666 is conductive dueto multivibrator 526 being triggered, the current through resistors 69S,:10 and 626 and the emitter-col lector junction of transistor 6%produces a voltage drop across resistor 69% which is substantially equalto that produced thereac oss when transistor 684 was conductive. Thus,when either transistor 604 or transistor 636 is conductive, the anode ofdiode 556 connected to the common junction terminal between resistors 6%and 61% via conductor 614, is always biased at the blacker-than-blacklevel.

When transistor 6% is conductive, the potential at the collector oftransistor 606 is at the same potential as that of the emitter oftransistor ch -2, or the block level, due to the resistance of. resistor612 being equal to that of resistor 626. The cathode of diode 5523 isbiased at the black level as long as transistor 6% remains conductive.The potential applied to the cathode of diode Si"), is at the blacklevel and any charge on capacitor more positive than the black levelcauses diode to become forward biased. Capacitor 54b discharges throughdiode 55 2 until the charms on capacitor 549 and the potential of theanode of diode 552 reach the potential of the cathode of diode 552. Theclamping of the potential on capacitor 549 at the black level before theend of the horizontal blanking signal insures that the following picturesignal will be referenced. to the black level.

Concurrently, the base of transistor 568 is clamped at the black levelby diode 552. At the end of the back porch clamping interval,multivibrator 526 reverts back to its stable state wherein transistor 6%is again conductive and transistor 6% nonconductive.

In summary, when the transducing head 16 reproduces the recorded videosignal from the oblique tracks, the reproduced video signal contains thehorizontal synchronizing and blanking signal in proper sequence relativeto the picture signal. The clamp and blanking unit 526, thesynchronizing signal stripper 524 and the multivibrator 526 function toclamp the back porch portion of the blanking signal at the black level,such that the following picture signal is referenced to the black level.Additionally, the blacker-than-black level for the horizontalsynchronizing signal is established by a clamping diode such that afollowing horizontal synchronizing signal will have the tip thereofclamped at the blacker-than-black level. Further, the back porch time isselected to be of sufiicient time duration such that the appropriateblack level is reestablished for the subsequent picture signalcorresponding to the next horizontal scan line.

As the reproduced video signal reaches the end of a field or one-halfframe, transducin head 16 crosses over and reproduces the signalsrecorded along the longitudinal edge of the recording medium. As thehead 15 approaches the edge of the recording medium, it is necessarythat a blanking signal be generated to insure that the reproduced signalis not passed or transmitted to the video output device 522. Theclamping pulse head 536 produces a clamping pulse in response to magnet86 being passed thereby. The clamping pulse is amplified by amplifier538 and applied to the multivibrators 52S and 530 to produce thevertical blanking and vertical synchronizing signals in proper sequence.

The pulse amplifier 538 comprises a single transistor whichsimultaneously triggers both multivibrators 528 and 539 in response tothe clamping pulse from head 536.

Multivibrator 53:), when triggered, clamps the cathode of diode 544 andthe base of transistor 553 at the blackerthan-black level. Themultivibrator 53% remains in its run stable state for a time intervalsubstantially equal to a veitical synchronizing signal interval, whichinterval is about equal to the time required for transducing head 16 tocross over the longitudinal edges of the recording medium 1'7.Concurrently, multivibrator 52% when triggered, applies a potentialsubstantially equal to the black level via conductor 632, to the emitterof transistor 56 Since the base of transistor is clamped at theblackerthan-black level via diode 54-4, transistors 55S and 566 of theDarlington pair remain in the nonconductive state. However, the voltageapplied to the emitter of transistor 56% produces a voltage drop acrossresistors S66 and 568 such that the potential of the base of thetransistor 574 is at a potential substantially equal to that of be blacklevel. Transistor 574, via resistor 5'73 and conductor 580, applies avertical blanking signal at the black level to the video output device5122 until multivibrator 528 resets.

Multivibrator 52% remains in its unstable state for a time intervalapproximately equal to the time required between the leading edge of thevertical blanking signal and the leading edge of the verticalsynchronizing signal. In one embodiment, the time interval was selectedto be approximately 600 microseconds. When the muitivibrator 52 3 resetsto its stable state, the clamping signal being applied to the emitter oftransistor 56% changes from the black level to the blacker-than-blacklevel established by the multivibrator 53:0 and applied to the base oftransistor 558. The base of transistor 558 remains clampedat heblacker-than-black level until multivibrator 53% re sets. The base oftransistor 553 is clamped at the blackerthan-black level for a timeperiod equal to a vertical synchronizing signal or until the head 16 isin alignment with an adjacent oblique track. During this time interval,capacitor 540 discharges through diode 552 and resistor 626 of themultivibrator 526 such that at the end of the vertical synchronizinginterval, capacitor 540 is dis charged to the blacker-than-black level.

In summary, as the transducing head 16 crosses the longitudinal edge ofthe recording medium 17, magnet 8:! causes the clamping pulse head 532to produce a clamping pulse which initiates the vertical blanking andsynchronizing signal. The clamp and blanking unit 520 is immediatelyclamped at the blacker-than-black level by the multivibrator 53d anddiode 544. Multivibrator 5Z3 raises the level of the signal applied tothe video output device 522 to the black level for a period equal to thetime interval between the leading edge of the vertical blanking signaland the time when the vertical synchronizing signal should be inserted.Multivibrator 52S resets beginning the vertical synchronizing signalwhereby the video signal is clamped at the blacker-than-black leveluntil the beginning of the next picture signal containing informationfor the beginning of the next horizontal scan line.

During reproduction of the recorded video signal, the speed of rotationof head 16 is controlled in response to the control signal recordedalong the longitudinal edge of the tape and a head position pulseproduced in response to the rotation of head 16. The synchronizing head21 reproduces and applies the control signal to a linear DC. amplifier113. The linear D.C. amplifier 113 may con prise any known amplifiercapable of amplifying the pulse to a predetermined level and theamplifier illustrated schematically in FIGURE 9 need not be recited indetail since the electrical connections and operations thereof are knownin the art. The amplifier 1Z3 applies the amplifier control pulse via aconductor 636 to the comparator 414. Concurrently, the comparator 414receives a head position pulse from amplifier 82 which receives thepulse from head 81. Comparator 414 produces a resultant signal orvoltage signal the magnitude of which is dependent on the phase relationof the signals. The resultant signal is subsequently applied to a leadnetwork and amplifier 490. The lead network and amplifier 4% produces abraking voltage which is applied to the braking winding 43 of thebraking motor 39 such that the rotation of the transducing head 16 is insynchronism with the oblique tracks recorded on a recording medium 17.

CONCLUSION It will be seen that I have provided a tape recorder forrecording and reproducing video signals in which the amount of tapeneeded is greatly reduced due to the head assazsi being rotated at anangle to the direction of movement of the tape and in which the signalis recorded and reproduced without loss of clarity in spite of therelatively slow speeds that are employed with such an arrangement. I,moreover, have provided such an arrangement in which the signal isdirectly recorded on the tape without the use of frequency modulation.This is accomplished by the novel use of various clamping circuits whichserve to restore any low frequency components that are lost and whichserve to re-insert the vertical synchronizing signal that is lost in therecording process.

It will also be seen that I have employed a novel comparator circuitwhich permits the transducer head to come up to speed very rapidly andthereafter controls accurately the relative position of the head withrespect to the video signal during recording or with respect to acontrol synchronizing signal produced as a function of the longitudinalspeed of the recording media during reproducing.

It will also be seen that I have provided a novel mounting for arecording head in which the head projects only slightly beyond thesurface over which the tape passes but in which the tape is held closelyin association with the head.

While I have shown a specific embodiment illustrating the teachings ofmy invention for purposes of illustration, it is to be understood thatthe invention is to be defined by the appended claims.

What is claimed is:

1. In a transducing system for recording and reproduc ing high frequencysignals utilizing a recording medium which is driven longitudinally at aconstant speed adjacent a transducing head rotating at a relatively highspeed with respect to the longitudinal direction of movement of saidrecording medium and at an angle to the longitudinal direction of therecording medium such that the head moves in oblique tracks across saidrecording medium, said system including control means for synchronizingthe head position with the oblique track positions across said recordingmedium comprising:

means for producing a control signal derived from said high frequencysignal; means responsive to said rotating head for generating a headposition pulse for each revolution of said head;

means operatively coupled to said control signal producing means andsaid head position pulse generating means for comparing the phaserelation between said control signal and said head position pulse anddeveloping a resultant signal whose magnitude is dependent upon saidphase relation; and braking means responsive to said resultant signalfor producing a braking force in a direction which regulates the speedof rotation of said head to synchronize the head position with theoblique track positions across said recording medium. 2. The transducingsystem of claim 1 further includmg:

means responsive to said control signal for producing a series of spacedvarying voltage pulses the amplitude of each of which steadily changedin an upwardly sloping direction during at least a portion of the pulseduration and in a downwardly sloping direction during a differentportion of the pulse duration;

means responsive to said head position pulse for producing a series ofspaced uniform voltage pulses having a predetermined polarity theamplitude of each of which remains substantially constant during atleast a portion of the pulse duration;

said comparing means being responsive to said varying voltage pulses andsaid uniform voltage pulses for comparing the phase relationtherebetween and for developing a voltage signal the magnitude of whichis dependent upon said phase relation and the amplitude of said varyingvoltage pulses.

3. The transducing system of claim 1 wherein said control means includestransducing means: for recording a video signal having synchronizingsignals in oblique tracks across said recording medium and wherein saidcontrol signal producing means includes a vertical synchronizing signalstripper and an integrator for deriving said control signal from eachvertical synchronizing signal of said video signal and at a frequencyequal to the frequency of said vertical synchronizing signal.

4. The transducing system of claim 1 wherein said control means includestransducing means for reproducing a video signal having synchronizingsignals recorded in oblique tracks across said recording medium andmeans responsive to said rotating head for generating a verticalclamping pulse each time said head crosses the longitudinal edges ofsaid medium, and wherein said means for deriving a control signal isresponsive to a control signal having a frequency equal to the frequencyof vertical synchronizing signals of said video signal recorded alongthe longitudinal edge of said recording medium.

5. In a transducing system for reproducing a video signal, havingsynchronizing signals and blanking signals, recorded in a series ofoblique tracks on a recording medium and a control signal recorded alongone of the longitudinal edges of said recording medium, said recordingmedium being driven longitudinally at a constant speed in a helical pathabout a transducing head which is rotated obliquely at a relatively highspeed with respect to the longitudinal direction of movement of saidrecording medium, said system comprising:

means for generating a first pulse for each revolution of thetrvansducing head and a second pulse as said head crosses the edges ofsaid recording medium;

ieans for reproducing said control signal from said one longitudinaledge of said recording medium, said control signal being representativeof the positions of said oblique tracks on the recording medium;

control means operatively connected to said pulse generating means andsaid control signal reproducing means for comparing the phase relationof said first pulse with said control signal to regulate the rotation ofsaid head to maintain alignment between said head and each obliquetrack;

electrical circuit means including clamping circuit means electricallyconnected to said head for receiving and passing reproduced recordedsignals and to said pulse generating means for receiving said secondpulse, said clamping circuit means being responsive to said second pulsefor inhibiting said electrical circuit means to prevent passage of thereproduced recorded signals as said head passes said edges of therecording medium;

said clamping circuit means inhibiting said electrical circuit means fora time interval about equal to the time interval required for said headto cross said edges of said recording medium into alignment with anadjacent oblique track.

6. The reproducing apparatus of claim 5 further including:

means responsive to said control signal for producing a series-of spacedvarying voltage pulses the amplitude of each of which steadily changesin an upwardly sloping direction for at least a portion of the pulsesignal and in a downwardly sloping: direction during a different portionof the pulse signal;

means responsive to said first pulse for deriving from said first pulsesa series of spaced varying voltage pulses the amplitude of each of whichis substantially constant and of the same polarity during at least aportion of the first pulse signal;

said control means being responsive to said varying voltage pulses andsaid substantially constant pulses for producing resultant voltage themagnitude of which is responsive to the phase relation therebetween andto the amplitude of the varying voltage pulses and being operative tovary the speed of rota-

